2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/140836We prove that the normalizer of any diffuse amenable subalgebra of a free group factor $L(\Bbb F_r)$ generates an amenable von Neumann subalgebra. Moreover, any II$_1$ factor of the form $Q \vt L(\Bbb F_r) $, with $Q$ an arbitrary subfactor of a tensor product of free group factors, has no Cartan subalgebras. We also prove that if a free ergodic measure preserving action of a free group $\Bbb F_r$, $2\leq r \leq \infty$, on a probability space $(X,μ)$ is profinite then the group measure space factor $L^\infty(X)\rtimes \Bbb F_r$ has unique Cartan subalgebra, up to unitary conjugacy.27 pages; minor modifications; 10/27/07: New version with improved statements, new applications, and simplifications in proofsOperator AlgebrasGroup Theory46L10 (Primary); 37A20 (Secondary)text